The present invention generally relates to an apparatus, system and method for determining wear and the rate of wear of an article such as for example a carbon brush, a brake pad or tire.
Dynamoelectric machines such as direct current (DC) motors use carbon brushes to provide a means for transferring current from an external source to a rotating armature of the motor. The brushes are typically made of a carbon particulate such as graphite and a binder material and may also include metallic particles.
These brushes are typically spring loaded to maintain good electrical contact with a commutator (i.e., slip ring) of the motor. A follower spring is employed to apply a biasing force against the rear end of the brush to cause the other end of the brush to be pushed into contact with the commutator. Since the commutator is in motion with the brushes in contact therewith, the brushes wear down over time. Consequently, these brushes must be replaced before they are completely worn in order to protect the commutator of the motor against damage. Alternating current (AC) machines may similarly employ brushes and commutators for the transfer of electric power and have similar brush wear problems.
Because the operating life of carbon brushes depends, respectively, upon the type of operation and environmental conditions of the installed motor and the desire to utilize the brushes to the maximum possible extent without risk to the commutator, it is good practice to monitor the carbon brushes for a predetermined amount of wear.
Cut-off carbon brushes are occasionally employed which automatically switch off a motor drive when a predetermined amount of wear of the carbon brushes has been reached. However, in the absence of expensive and time-consuming intermediate inspections, it is unforeseeable when the motor drive will be switched off. As a result, a process incorporating such a device must take into account the risk of unexpected shutdown of the motor drive due to brush wear.
Carbon brushes with alarm devices which provide an early warning of the failure due to wear are available. These devices typically include an alarm contact provided by an electrical conductor (e.g., a copper strand) baked into the upper end of the carbon brush by the commutator. When the brush wears by a predetermined amount, the electrical conductor contacts the commutator (or slip ring) which serves to complete an electric circuit or, as by wearing through a loop at the end of the conductor, break an existing circuit. A problem with such a device is that the electrical conductor may cause some damage to the commutator surface if exposed to it for an extended period of time as a result of metal to metal contact. Furthermore, such devices only alert a user that the brush has reached a particular level of wear - such alarm system does not provide a user with the rate of wear of the carbon brush or any type of intermediate evaluation.
Another type of article that is prone to frictional wear is a brake pad. Brake pads in automobiles, for example wear through usage and require periodic replacement. Inspection of brake pads requires the removal of the wheel from the vehicle so that a visual examination may be performed. Many individuals are unwilling and/or unable to perform the inspection or not skilled enough to know what to look for when the wheel is removed.
Many vehicle owners may rely on a dashboard trouble light to indicate when brakes need replacement. However, this trouble light is present to monitor the hydraulic braking system through brake fluid pressure and does not monitor brake pad wear. A squeal from the brakes may be a warning, or may indicate that the rivets holding the brakepad to its backing are contacting a rotor or drum which can cause scoring of the rotor or drum. Should the pad be totally worn out, the noise would be from the pad backing contacting the rotor or drum, which would cause considerable damage to the rotor or drum.
Another article which is prone to wear is a tire for use in an automobile, for example. Tires wear as a result of frictional contact with road surfaces. Furthermore, tires are prone to other problems in connection with pressure and temperature. An improperly inflated tire or worn tire may be manifested as reduced efficiency in gas mileage, reduced performance in ride and handling, reduced performance in vehicle braking, reduced cornering ability, and potential blowout or other catastrophic failure.
Additionally, conventional techniques for monitoring pressure and temperature information relating to an article and/or an environment such as, for example, in a carbon brush or pump chamber often prove to be expensive and/or cumbersome.
In view of the above, there is a strong need in the art for an improved apparatus, system and/or method for determining wear and the rate of wear of an article such as a carbon brush, brake pad or tire, for example. Furthermore, it would be highly desirable to have such an apparatus, system and/or method which can also determine pressure and/or temperature information relating to the article.
The present invention employs an optical fiber to facilitate the measure of wear and the rate of wear of an article that the optical fiber is embedded in. By embedding at least one optical fiber into the article, information relating to the wear and rate of wear of the article can be obtained. For example, in the case of a carbon brush of a dynamoelectric machine, an optical fiber is embedded into the carbon brush in order to obtain such wear data. As the article (i.e., carbon brush) wears so does the optical fiber which has its length direction disposed substantially parallel to the direction of wear of the article.
A light beam is directed into one end of the optical fiber and the light is transmitted through the optical fiber to the surface of a commutator which the brush is in contact with. The light is reflected off the surface of the commutator and transmitted back through the optical fiber. The present invention employs interferometric techniques to analyze the transmitted light signal (i.e., measurement signal) and a reference signal. From the interferometric techniques, information relating to the wear and rate of wear of the fiber optic cable can be determined. Since the optical fiber is substantially weaker than the article it is disposed in, the wear and rate of wear of the optical fiber is substantially that of the article. Thus, wear and rate of wear of the article can be conveniently determined. Wear and rate of wear may be determined extremely accurately with a precision of a fraction (e.g. {fraction (2/10)}) of the wavelength of the transmitted light beam. Furthermore, most dynamoelectric machines employ a multitude of brushes (perhaps 8 or more). The present invention affords for sharing a common light source and some sensing devices.
The aforementioned technique may be employed to analyze wear and rate of wear of a variety of articles including brake pads and tires. For example, an optical fiber may be embedded in a brake pad such that as the brake pad wears so does the optical fiber in its length direction. By using interferometric techniques as discussed herein, the amount of wear and the rate of wear of the brake pad can be determined. Likewise, the amount of wear and the rate of wear of a tire can be determined employing a similar technique.
Additionally, the present invention provides for determining other information such as that relating to surface assessment, article related temperature and/or environmental pressure, motor speed, and article related pressure and/or environmental related pressure.
Light reflected off a surface of something the article is in contact with will have encoded therein data relating to the condition of the surface. Thus, if the article is in contact with a commutator surface for example, the light reflected off the surface of the commutator will change in intensity relative to the passing of the commutator bars and slots and to the condition of the commutator surface. This change in light intensity can be used in accordance with the present invention to determine the condition of the commutator surface (which tend to exhibit changes in reflectivity).
Additionally, an optical fiber having a temperature-sensitive index of refraction in conjunction with a periodic grating structure may be used in accordance with the present invention to determine change in temperature of an article and/or the environment. A change in the index of refraction due to a temperature change will cause a shift in a peak transmission/reflection wavelength of the light being reflected back off the surface. Temperature estimates of the medium (e.g., article body or environment) surrounding the optical fiber may be made by analyzing the attenuation of the reflected light signal at specific wavelengths.
Furthermore, the present invention may be employed to determine the speed of a motor. Time-based frequency measurements of the reflected light beam pulses off the commutator bar surfaces may be employed to provide indication of motor speed.
The present invention may also be used to determine pressure information. An optical fiber will undergo micro-bending as a result of pressure applied thereto. The affect of this bending is an attenuation of the transmitted light signal, which varies in relation to the amount of bending of the optical fiber. Accordingly, the optical fiber can be employed to provide pressure data relating to an article/medium it is exposed to. For instance, if the optical fiber is embedded in an article such as a carbon brush, the optical fiber can provide data relating to the pressure the carbon brush is exposed to. Similarly, if the optical fiber is placed in an environment such as a pump chamber, the optical fiber can provide data relating to the pressure within the pump chamber. Additionally, by exposing the optical fiber to the interior of a tire, for example, pressure information relating to the inflation of the tire may be obtained.
In accordance with one specific aspect of the present invention, a system for determining wear of an article is provided and includes: an optical fiber for transmitting light from a light source, the optical fiber being embedded in the article; and an interferometric system operatively coupled to the optical fiber and a processor; wherein the interferometric system provides the processor with information relating to wear of the optical fiber, and the processor determines wear of the article based on the information.
According to another aspect of the present invention, a system for determining wear of an article is provided and includes: a light source for generating a primary beam; a beam splitter for receiving the primary beam and splitting the primary beam into a reference beam and a measuring beam, the beam splitter directing the reference beam to a mirror; an optical fiber at least part of which is embedded in the article, the optical fiber having first and second ends, the first end receiving the measuring beam, the second end being flush with a contacting surface of the article, the article being in contact with a surface; and a detector for detecting an interference beam from the beam splitter, the interference beam comprising a reflected reference beam and a reflected measuring beam, the detector transforming the interference beam into an electrical signal; and a processor for receiving the electrical signal, the processor determining wear of the article based on the electrical signal.
Another aspect of the present invention provides for a system for determining temperature related information of an article which includes: an optical fiber for transmitting light from a light source, the optical fiber being embedded in the article, the optical fiber having a temperature-sensitive index of refraction, and being operatively coupled to a temperature sensor, the temperature sensor being adapted to receive at least a portion of a measuring beam being transmitted through the optical fiber, the temperature sensor being operatively coupled to a processor, the temperature sensor providing the processor with data based on the measuring beam, and the processor determining temperature related information based on the data.
Still another aspect of the present invention provides for a system for determining pressure of an article which includes: an optical fiber for transmitting light from a light source, the optical fiber being embedded in the article, the optical fiber having at least one induced microbend, and being operatively coupled to a pressure sensor, the pressure sensor being adapted to receive at least a portion of a measuring beam being transmitted through the optical fiber, the pressure sensor being operatively coupled to a processor, the pressure sensor providing the processor with data based on the measuring beam, and the processor determining pressure related information based on the data.
Another aspect of the present invention provides for a carbon brush for providing current to a commutator of a dynamoelectric machine, the carbon brush having at least one optical fiber embedded therein.
In accordance with another aspect of the present invention, a method for determining wear is provided and includes the steps of: using an article having an optical fiber embedded therein; using an interferometric system operatively connected to the optical fiber to collect information relating to the optical fiber; and using a processor operatively coupled to the interferometric system to determine wear of the article based on the information.
Still yet another aspect of the present invention provides for a system for determining a condition of an object which includes: an optical fiber for transmitting a measuring light beam toward the object and for transmitting at least a portion of the measuring light beam reflected back from the object; a signal monitor operatively coupled to the optical fiber and a processor, the signal monitor adapted to receive the reflected measuring light beam; wherein the signal monitor provides the processor with information based on the reflected measuring light beam, and the processor determines a condition of the object from the information.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.